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requires a great deal of care. In this acid, care being taken 
to exclude all atmospheric air, pure zinc was dissolved. No 
generation of gas could be observed, and the fluid, after 
deepening gradually in color so as to become at last quite 
brown like old sulphide of ammonium, commenced to sepa- 
rate sulphur, regaining its original colorless state after some 
time.* 
While brown, and before sulphur had commenced to sepa- 
rate, part of the fluid was saturated with caustic potassa, and 
tested for sulphur (as sulphide of potassium with nitro- 
prusside of sodium), which was proved to be absent. After 
repeatedly shaking the fluid, which had become milky from 
separated sulphur, the solution itself being quite colorless, 
and allowing it to stand for several hours, a small amount of 
it was taken and tested in several ways. It contained still 
an excess of sulphurous acid, which, I may mention here, does 
not disappear even after standing for several weeks with 
metallic zinc, owing to the zinc becoming covered with a 
coating of sulphide of zinc, a trifling amount of which is 
always formed in this operation; part of it may be seen 
floating about in the liquid. Upon acidulating a part of the 
solution in question with hydrochloric acid and heating, 
sulphur separated in large quantities and of a yellow color, 
while sulphurous acid was given off; another portion was 
acidulated with the same acid and left standing; in a few 
minutes sulphur separated, increasing in quantity while 
standing, and sulphurous acid being given off again. This 
established the presence of hyposulphurous acid, as no 
* The few bubbles of gas escaping at the beginning are very probably 
carbonic acid. Zine, like many other metals, oxidizes in moist air, be- 
coming thereby converted into basic carbonate. A stick of zinc, which 
had been cleaned beforehand with a file, so as to present a pure metallic 
surface, did not show the phenomenon of generating gas. Ordinary 
granulated zine (which is always coated with a whitish oxy-carbonate) 
shaken with water imparts to it an alkaline reaction, on account of the 
carbonate dissolving to a perceptible extent, and which may be easily 
tested with solution of cochineal. The amount of carbonic acid which 
all metals absorb, when exposed to the oxidizing influence of moist air, 
is accounted for by the fact that it dissolves to a much larger extent in 
moist air than would correspond to 1°25 of a per cent., and that it very 
likely exists in this solution as carbonic acid and not as anhydride. 
